Jerry Coyne explains why the proposed idea of a single pair of original human ancestors is refuted by what we know of our evolutionary ancestry:
Over at the Templeton-funded BioLogos website there has been a lot of discussion about the historicity of Adam and Eve. This is a problem because scripture claims these two were the progenitors of humanity, but genetics says otherwise. It’s simply not true that all of humanity’s DNA traces back to a pair of individuals who lived no more than 10,000 years ago; indeed, the different bits of our DNA trace back to different ancestors who lived at different times. What’s clear is that our ancestors were in a population of humans, some of whom left Africa around 60,000 years ago, and virtually all of modern human DNA comes from that population, which itself descended from African ancestors who split off about 6 million years ago from the ancestors of modern chimps.
For some reason the biological data have caused a kerfuffle at BioLogos. One would think that if these folks are really devoted to reconciling science and Christianity, they’d do for Adam and Eve what they did for Genesis: claim that this is just a metaphor rather than the literal truth, and the literal interpretation is theologically misguided. Adam and Eve simply stood for our ancestors, just as Smokey the Bear stands for all wild bears. (No matter that for centuries Christians wrongly assumed what the Bible says plainly: Adam and Eve were the two God-created ancestors of all humanity.)
He goes on to pick apart the stubborn and pathetic theories offered by those who want to cling to the belief in a literal Adam and Eve, rather than just change their reading of the story to a strictly metaphorical one. Of course I do not think even a metaphorical reading of Adam and Eve can be shown to be divinely true, as I have explained at length. But it’s at least a sane and science respecting strategy, unlike what is required to make the literal reading at all square with known reality.